PREFACE TO THE SECOND EDITION 7 



do most of the work here outlined for the dissection of the 

 dogfish head and sheep and human brains and for the study of 

 the microscopic sections as directed, the sections being sup- 

 plied from the departmental loan collection. The " optional 

 dissections" of the human brain (sections 102 to 111, 141 to 

 152) are omitted, or are done by some students in extra time 

 or in a more advanced course. 



The second edition has been entirely reset and the references 

 to literature brought up to date. Some other minor changes 

 have been made, in particular new blocks for Figures 5A 

 and 5B, which have been revised by Norris and Hughes 

 in conformity with the latest results of their investigations. 

 Our especial thanks are due to them for their care in this 

 matter and to numerous others whose kindly criticisms have 

 been very helpful. 



THE AUTHORS. 

 CHICAGO, ILL., 

 November, 1919. 



